3.3.4. EAG recording

After the
insect antenna or sensory organ has been successfully mounted, start recording
the signal on the computer monitor. A stimulus should only be applied when a
relatively stable baseline signal is obtained.

Depending
on the nature of the application of the stimulus, EAG recordings can either be
described as continuous or discontinuous. A continuous recording involves the
continuous application of the stimulus over the antennal preparation throughout
the recording session while a discontinuous recording refers to the application
of stimulus at intervals. Coupled gas chromatography electroantennographic
detection (GC-EAD) is the most widely used technique for continuous recording.

Coupled
GC-EAD recordings can be used to record antennal responses to both natural and
synthetic mixtures of chemicals. The GC chemically separates the mixture into
individual components which are then detected by the antenna, followed by
identification of the antennally-active components by coupled gas
chromatography-mass spectrometry (GC-MS).
However, a coupled GC-EAD system is expensive to setup and run, bulky
and requires lengthy recording times. Compared to continuous GC-EAD recording,
discontinuous EAG recording is a simple, less bulky and fast way of testing
individual chemicals at different doses for antennal activity. Discontinuous
recordings are mostly used in dose response studies to compare antennal
responses to identified chemicals. This usually involves quantification of
responses to the various chemicals, averaging these responses and comparing
them using various conventional statistical tests (see the BEEBOOK paper on statistics (Pirk et al., 2013)). The drawback of this method is that it is not
suitable for testing mixtures of chemicals especially natural unidentified
mixtures, and it cannot be used to identify unknown compounds.

Both GC-EAD
and EAG recording systems complement each other and it is advantageous to have
both systems in place in any insect electrophysiology laboratory. A coupled
GC-EAD system can easily be converted into stimulus puff EAG recording system
by switching-off the GC and using the opening at the side of the metallic
stimulus delivery tube to puff odours over mounted antenna.